Component list is as follows:-

PIC 16F630. Optionally 16F676, 12F629 or 12F675 will fit on same footprint.
12F629 will probably be cheapest.
78L05 regulator
Q1-8    Standard NPN transistor such as BC182L
J3       Pin header to suit in circuit serial programming
R1,R2    10K 1%
R3,R4    1K 1%
R5-R12    4K7
R13,R14	 10K
R15	4R7 0.25W (use a higher power resistor e.g. 2W if it gets too hot!)
C1    1uF 35V (or larger if possible) electrolytic/tantalum
C2,C4    100nF ceramic
C3    470nF ceramic
D1,D2 1N4148
D4-D7 UF4001 or UF4003 (2A max decoder load) or 1N4148 (300mA max decoder load)
D3	27V zener diode such as BZY89C27 or 1N971B

There is a choice of four processors which all use the same firmware without
modification.

16F630 - Will give basic 8-function functionality (outputs A to D on J1, E-H
on J2).
16F676 - Can be software upgraded later to support asymetric braking if
anyone can think of a use for it in a function decoder.
12F629 - Same as 16F630 but only three function outputs (Outputs A,B and D
on J1)
12F675 - Same as 16F676 but only three function outputs (Outputs A,B and D
on J1)

The 8-pin chips can be fitted in the
14 pin footprint by aligning pin 1 of the 8-pin chip with pin 1 on the 14
pin footprint. When using an 8-pin processor there will be five less
transistors and resistors and one less connector.

I have not included provision for back up power (as in Lenz PS1) because I
think it complicates things. The 1% resistors are specified to allow the
processor to decode packets even if the track voltage drops to virtually
nothing for a short while (for instance during a momentary short circuit or
if a wheel goes over some dirt). The worse the tolerance of the resistors
the greater the effect of the intrinsic (non adjustable) voltage offset in
the on board comparator of the PIC. The circuit will work pretty well with
higher tolerance resistors, but better with lower tolerance ones.

New Features in V1.02
---------------------

Added circuit R14,D2,C4 to ensure that track signal appearing at the PIC is
between oV and 5V. This should allow the circuit to work with track voltage
down to well below 1.2V for a short while.


New Features in V1.03
---------------------

Corrected value of R3 and R4 from 2K7 to 2K2 to allow operation up to at
least 24V on the track

New Features in V1.04
---------------------

Added over voltage protection components to prevent component failure if
the peak track voltage exceeds 35V. This should ensure compatibility with
the Hornby Select.

New features in V1.05
---------------------

Adjusted values of R3 and R4 from 2K2 to 1K to allow better decoding performance at higher track voltages and to allow the use of 3.3V regulators instead of the 78L05 for better DC performance.
Changed the value of D4-D7 to allow the total decoder output to exceed 300mA.
Changed the value and rating of R15 to match that supplied in the kits.
Added the part numbers of the zener diodes supplied in the kits.
